It is well established that strong Deuterium enrichment takes place in molecular material of cold, dark and prestellar cores [1]}. The first evidence of molecular deuteration in L1157-mm were brought by [2]}, with the detection of the deuterated forms of HCN and HCO\(^+\) , and a molecular D/H ratio of 0.018 in the cold envelope.
Our own determinations, which are based on the modelling of a larger number of rotational transitions, yield a somewhat higher D/H ratio
\(0.06\pm 0.02\)  for both HCN and HNC, in rough agreement with [2]}.
